This invention is related to a display device, and more specifically to a drawing device.
An erasable drawing device is known. An erasable drawing device, typically, consists of a blackboard, paper pad, or white board, and an erasable marking device such as a chalk, pencil or dry-erasable marker.
One drawback of such drawing device is that the marking device can dissipate, requiring replacement. Another drawback is that the marking device can make marks on surfaces other than the screen of the drawing device, thereby creating a mess. Still another drawback is that the screen may not erase completely even with cleansers and vigorous erasing.
An electronic drawing device overcomes some the problems described above. An electronic drawing device, typically, includes a touch screen and appropriate logic to cause an underlying electronic display to update its image in response to the motion of a stylus. The device, for example, includes a graphics input pad having an array of transparent capacitive pixels, which change their capacitance in response to a conductive tipped stylus passing over the pad. The change in capacitance is sensed and used to address an LCD matrix. A drawback of this electronic drawing device is that it requires sophisticated electronics and significant amount of power. U.S. Pat. No. 4,639,720 describes an electronic drawing device.
A magnetophoretic display, typically used as children""s drawing toy, is another example of an erasable drawing device. In a magnetophoretic display, a stylus used to write on the display contains a magnet, and a contrast media on the display contains black ferrous material and white titanium dioxide. The magnetophoretic display requires no power. However, the magnetophoretic display does not typically permit the user to selectively erase portions of a drawing on the display, unless the user is able to access both the front and back of the magnetophoretic media. Typically, manufacturers of magnetophoretic displays simply provide access to only one surface. The display is erased using a sliding bar magnet embedded behind the magnetophoretic media. Therefore, the display cannot be selectively erased.
An electrostatically-addressed liquid crystal display is another type of drawing device known in the art. Liquid crystal drawing devices, however, suffer from poor image duration due to dissipation of the surface static charge which maintains the image. With higher voltages and additional resistive layers, it is possible to extend image duration, but even then, a duration exceeding 30 minutes is considered state of the art. U.S. Pat. Nos. 5,351,143 and 5,117,297, describe liquid crystal drawing devices.
An electrophoretic display is also used as a drawing device. In an electrophoretic drawing device, electrophoretic particles in a display media of the device migrate toward or away from the drawing surface of the device upon application of an electric field across the display media. For example, the drawing device can contain a back electrode covered by an electrophoretic coating. To write, a positive voltage is applied to the back electrode and a stylus contacting the electrophoretic coating is set at ground. The stylus acts as a top electrode in a local area. A voltage potential is created between the stylus and the back electrode which causes migration of the electrophoretic particles and a color change of the device. The overall system may be covered with a dielectric or anisotropic top layer that protects the electrophoretic media. Chiang et al. xe2x80x9cA Stylus Writable Electrophoretic Display Device,xe2x80x9d Society for Information Display 1979 Digest describes an electrophoretic drawing device. Although electrophoretic displays offer excellent contrast and brightness as well as favorable electrical properties and image duration, electrophoretic displays have not been broadly commercialized due to difficulty in manufacture and lifetime issues related to particle agglomeration and migration within the display.
In one aspect, the invention features a display. In one embodiment, the display comprises an encapsulated display media having a first surface and a second surface, a rear electrode disposed adjacent the second surface of the display media, and a movable electrode. The display media comprises a plurality of capsules, each capsule comprising a plurality of particles dispersed in a fluid. The movable electrode, in conjunction with the rear electrode, applies an electric field across the display media.
In one detailed embodiment, the movable electrode comprises a writing device. The writing device can comprise a charge generator. The charge generator can comprise an electronic circuit capable of increasing a voltage from about 20 V to about 1000 V. The charge generator can further comprise an electronic circuit, which reduces an applied voltage to zero after a predetermined time interval. The writing device can comprise a charge storage device. The writing device can comprise a stylus. For example, the stylus can comprise an electrode tip disposed within a curved end of the stylus. The stylus can further comprise a plurality of concentric electrodes. The writing device can include an activator, such as a piezoelectric device, which activates the charge generator. The writing device can have a first end and a second end. The display media displays a first color when the first end is disposed adjacent the first surface of the display media and a second color when the second end is disposed adjacent the first surface of the display media.
In another detailed embodiment, the movable electrode comprises an eraser. In still another detailed embodiment, the movable electrode comprises a user touching the first surface of the display media. In still another detailed embodiment, the movable electrode comprises a sliding bar, which slides across the first surface of the display media. The sliding bar can include a charge generator, an activator which activates the charge generator, an electrostatic print head, and/or a scanner. The charge generator can be a Van de Graaff device, a triboelectric mechanism, or a hand-driven electric generator. The sliding bar can communicate with a data storage device. Alternatively, the sliding bar can comprise a data storage device.
In still another detailed embodiment, the movable electrode comprises a switch, which reverses an electric field applied to the display media upon activation of the switch. For example, a color displayed on the first surface of the display media can change upon activation of the switch.
In one embodiment, the rear electrode comprises a first region having a voltage different from a voltage of the movable electrode and a second region having a voltage :matching the voltage of the movable electrode. In another embodiment, the rear electrode comprises a conductive pattern. In still another embodiment, the display media comprises a plurality of electrophoretic particles comprising a plurality of colors, and the rear electrode comprises a plurality of pixel electrodes, each pixel electrode being set at a voltage for displaying particles of a selected color on the first surface of the display media. Alternatively, the rear electrode can be movable.
In another detailed embodiment, the display further comprises a touch screen disposed adjacent the first surface or the second surface of the display media. The touch screen can be laminated to the display media.
In another embodiment, the display comprises a display media forming a continuous loop, and an electrode disposed inside the continuous loop of the display media. In one detailed embodiment, the display further comprises a case containing the display media and the electrode. The case has a first surface and a second surface. The first surface comprises a protective layer and serves as a writing surface. In another detailed embodiment, the display further comprises a movable electrode. The movable electrode, in conjunction with the electrode, applies an electric field across the display media.
In still another embodiment, the display comprises a display media having a first surface and a second surface, an electrode disposed on the first surface of the display media, and a photoconductor disposed on the second surface of the display media. The display media displays a replica of an image shown on a substrate when the photoconductor is provided adjacent the substrate. In one detailed embodiment, the substrate comprises an emissive display such as a computer screen or a television screen.
In another detailed embodiment, the substrate comprises a reflective display. The reflective display can be a piece of paper. In another detailed embodiment, the display further comprises a light source for illuminating the substrate.
In another aspect, the invention features a method for creating an image on a display. The method comprises the steps of: (a) providing a display comprising an encapsulated display media comprising a plurality of capsules, each capsule comprising a plurality of particles dispersed in a fluid, the display media having a first surface and a second surface and a rear electrode disposed on the second surface of the display media; (b) placing a movable electrode adjacent the first surface of the display media; and (c) applying an electric field across the display media through the movable electrode and the rear electrode, thereby creating an image on the first surface of the display media.
In another aspect, the invention features a method for reproducing an image. The method comprises the steps of: (a) providing a display comprising: a1) a display media comprising a first surface and a second surface, a2) an electrode disposed on the first surface of the display media, and a3) a photoconductor disposed on the second surface of the display media; and (b) placing the photoconductor adjacent a substrate comprising an image, thereby reproducing the image from the substrate on the display media.